Hi I have some very important differential pairs on a PWB that must have a particular differential impedance. The problem is: how can I specify this on the drawing sent to the fab shop? Our usual method would be to call for a particular single-ended impedance, which seems to be beating around the bush. It work to a point; but I think it leaves too many variables that could change the differential impedance. Any thoughts on this? Joe Hurst PWB Designer Computing Devices Canada A General Dynamics Company [log in to unmask] 613-596-7816 ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################